The invention relates generally to the field of automatic irrigation systems and more specifically, to irrigation systems which maintain the proper degree of soil moisture by measuring the soil moisture with in-ground probes and, when needed, activating irrigation sprinklers for a pre-set period of time.
There is a need for greater sophistication in the field of irrigation management. There are many factors which determine periodicity with which a field or an orchard needs water, such as temperature, wind conditions, humidity, and the maturity of the plants. Over the course of the growing season, the periodicity will, of course, change. With the greater stress on productivity of farming, it is essential to eliminate the damage caused to crops by over or under watering. Further, with many areas of the country experiencing water shortages, it is more necessary than ever to limit watering to only when it is actually needed.
In the past, there have been several methods for monitoring soil moisture, but none have been totally satisfactory. These methods are normally based on the measurement of physical properties related to the water content of the soil, most normally electrical properties. One of the most popular methods is based on measuring the electrical conductivity of the soil. But, electrical conductivity changes with other factors than moisture, such as the salinity of the soil. Further, the electrical current tends to degrade the electrodes by electrolysis and by chemical reaction with components within the soil, especially fertilizers.
The present invention measures the physical property of heat conductivity. It is based on the natural phenomenon that air is a good heat insulator, whereas water is a good conductor of heat. Similarly, when wet a porous element of the in-ground probe dissipates heat relatively quickly, whereas when the water has been replaced by air it dissipates heat relatively slowly. The porous element, being in physical contact with the soil, has virtually the same moisture content as the soil. By comparing the heat conductivity of the porous element to a given standard, one can tell the moisture content of the soil.
This invention fulfills the need for more sophisticated irrigation management equipment. It takes advantage of microelectronics to keep the price low, the speed with which measurements taken high, and the accuracy high. The system is relatively maintenance free and highly corrosion resistant. Further, the system is not effected by salinity, or other ionization conditions of the soil and under the environmental conditions of normal use would not be effected by freezing weather.
Among the advantages of the present invention is that it corrects automatically for temperature. Regardless of the temperature of the soil, the readings are still accurate.
Another advantage of the present invention is that it uses microelectronics which provide speed and accuracy at a relatively low price, freedom from maintenance, long life, and a relatively low amount of energy usage.
Another advantage of the invention is that it can be used to test the soil only at intermittent periods. This saves power because power can be supplied to the probe for a relatively short fixed period, spaced apart by relatively large intervals. This lengthens the life of the in-ground probe, reduces power consumption, and increases measurement accuracy.
Another advantage is that the invention is able to record moisture readings from many probes and control irrigation based on soil moisture tests on a plurality of regions in the field.
Another advantage is that the invention is amenable to solar/storage battery powered operation. For long periods, only a timer need be powered with intermittent short periods of greater power being drawn by the sensor probe's heating element.
Another advantage is that the invention makes checking soil moisture much simpler than in the past and removes the need for manual handling of equipment. This allows a large number of measurements at each of a large number of locations to be taken each day.
Another advantage is that the invention irrigates for an adjustable, preselected period of time. There is no need to activate the probes to control the irrigation shutoff. If the preselected interval should supply insufficient water, the irrigation period will be repeated after the next measurement cycle.
Another advantage is that the probes can be installed permanently in their under ground position because they are of such a long life, have such a freedom from maintenance, and are resistant to freezing.